Magnetic and Thermal Properties of Tb(OH)3

Abstract

Low-temperature measurements of magnetic susceptibility, magnetization, and specific heat have been made on single-crystal and polycrystal samples of Tb${\mathrm{}\left(\mathrm{OH}\right)\mathrm{}}_3$. The experimental techniques and methods of analysis were similar to those used previously to study isostructural Gd${\mathrm{}\left(\mathrm{OH}\right)\mathrm{}}_3$. The results are consistent with earlier reports that Tb${\mathrm{}\left(\mathrm{OH}\right)\mathrm{}}_3$ is a highly anisotropic ferromagnet resembling a three-dimensional Ising model, but a detailed analysis revealed an interesting range dependence of the effective spin-spin interactions. Estimates of the interactions between first-, second- and third-nearest neighbors were made from measurements at temperatures high and low compared with the Curie temperature ($T_C=3.72\mathrm{}\pm 0.01$ K), using asymptotically exact series expansions correct to second order, and for both the first- and second-nearest neighbors an unusual cancellation between the magnetic dipole and "exchange" interactions was found. As a result of this cancellation, the net interaction between second-nearest neighbors becomes comparable to that between the nearest neighbors, but both are reduced in absolute magnitude so that they become comparable to the long-range dipole interactions between more distant neighbors. Some consequences of this competition on the cooperative properties are discussed.